So, it means that the only thing I can really control with these lenses is shutter speed and ISO
Well you can still control aperture with the aperture ring ( and that used to be the way it was done all the time ! ). Having an aperture ring is an advantage in my view, but if you're not used to them they do seem strange.
A seasoned photographer who was used to not having all this automatic stuff (and can you trust it anyway???) will feel better, but beginners and amateurs will look to the manual and find no answers.
In fact you have more direct physical control of those lenses than with the "native" 4/3 lenses, which are all "fly by wire" - even when you turn the focus ring on a micro 4/3 lens you are actually requesting the camera and lens to do something rather than doing something.
Not so much different from when you press the shutter button. Potato potato.
Also those old lenses ( and some of these old lenses are very good
... and some aren't ...
) will be usable on many other systems via simple adapters.
... and still be manual lenses.
Don't feel you've been short changed with those lenses.
That very much depends on the price, IMHO. To release the full potential of the camera, you will need a compatible lens.
, and the different modes/scenes on the camera basically won't work unless I get a compatible lens?
Well I'd suggest you try them, but really all the scene modes are variations on Aperture Priority and Shutter Priority and you'll find that you don't need scene modes at all.
I don't know how your camera reacts to manual aperture lenses in the different modes. The Olympus forum would be the place to ask. Aperture priority mode could work as it sets ISO and shutter speed according to a fixed aperture.
Scene modes is a way to tell the camera how it should prioritise the compromises included in setting exposure. Learning about exposure will make it easier for you to expose manually and to understand what the scene modes does, but if you are not an experienced photographer, scene modes can be of help.
I think that nostalgia for the manual past is acceptable to those who master the craft of manual photography, but IMHO automation serves a purpose and frees the photgrapher's mind from calculations which is just as well made by a computer, leaving room for more deliberate composing and creativity. But it is just an opinion, worth no more or no less than others'.